1. Field of the Invention
The invention is generally related to a method for eliminating image noise and an apparatus using the same, more particularly to introduce an average of partial pixels and an allotment-compensation mechanism to be a basis for compensation, in order to eliminate the image noise as photographing.
2. Description of Related Art
A digital camera generally utilizes lens to capture an image and projects it onto an image sensor, such as CCD, CMOS. Through the image sensor, the image is converted into digital image signals. The digital signals are then stored into a storage medium via some electronic circuitries. A color filter is usually mounted in front side of the image sensor since merely the light intensity can be sensed by the image sensor but not the colors.
According to the conventional technology and its improvement, the mentioned color filter incorporates a color separation concept of the three primary colors (Red, Green, Blue). Generally, three separate image sensors in a conventional art are used to record three separate primary values, and then the values are mixed to form a true-color image. In particular, a single image sensor is also used since it utilizes the color filter to separate the incoming signals into three values of primary colors which are separately recorded by pixels. Each pixel only records one of the grey scales of the primary colors. After that, the pixels can be mixed as a true-color image.
In the mentioned design, one pixel only senses one color at one time and ignores the other two. An interpolation method will be introduced to re-establish the two lost colors.
It is noted that the color filter usually adopts a square-form filtering array, that is Bayer pattern.
The image captured by the digital camera having the image sensor may have noise because of the interference caused by the inside circuits or the defect within the image sensor. For example, the hardware design of the image sensor easily makes difference of the intensity between lines thereon. The difference may cause fixed image noise on the image along vertical direction and directly affect the image's quality. Therefore, when the digital camera is produced, some compensating values will be used for future photographing after the above examination.
In general, it's to take a picture from a uniform light source or an image, and to calculate a difference between each pixel and a line average. The compensation values for the pixels in each line are then obtained by dividing a sum of the pixels by the pixel number.
A magnification factor is calculated in accordance with the gain for G channel as photographing. The compensation value magnified according to the magnification factor will be subtracted for restoring the image after elimination of the fixed image noise.